Air and water resistance

This lesson covers: 

  1. How air and water resistance act as frictional forces
  2. The effects of air resistance on falling objects like parachutists

Air and water resistance

When objects move through air or water, a frictional force is exerted on the object called drag, that pushes against the motion.

Diagram showing a comparison between a not streamlined car with large air resistance and a very streamlined car with small air resistance.
  • Air and water resistance try to slow moving objects down.
  • More streamlined shapes can slip through the air or water easily with less drag.

Air resistance on falling objects

When a person parachutes from a plane, they experience changing air resistance and weight forces.

Illustration of a skydiver showing air resistance and weight forces with an aeroplane in the background.

1. When a skydiver first jumps from a plane gravity (weight) is more than air resistance, accelerating their downward fall.

Terminal velocity

Diagram showing air resistance and weight forces acting on a skydiver.

2. The skydiver's speed increases, causing greater air resistance pushing up.

3. Eventually the air resistance balances the weight and the skydiver falls at a constant speed - terminal velocity.

Unbalanced forces means a change in speed

Diagram showing a skydiver with a parachute experiencing balanced forces of air resistance and weight.

4. At a certain point, the skydiver opens their parachute, greatly increasing the air resistance.

5. The air resistance is more than the weight and so the speed at which the skydiver falls decreases.

Balanced forces means a steady speed

Illustration of a skydiver with a parachute showing air resistance and weight forces.

6. The upward air resistance grows equal to the downward pull of weight.

7. With balanced forces, the skydiver falls at a steady safe speed for landing.

Balanced forces can cause no movement

Illustration showing a skydiver landing with weight balanced by the upward force from the ground.

8. The skydiver lands safely and come to a stop as their weight is balanced with the upward force from the ground.